The invention concerns an apparatus for simultaneous detection of a plurality of spectral regions of a light beam, in particular for detection of the light beam of a laser scanner in the detection beam path of a confocal microscope.
Apparatuses for simultaneous detection of a plurality of spectral regions of a light beam have been known from practical use for some time, and are referred to as xe2x80x9cmultiband detectors.xe2x80x9d These are complex optical arrangements that use an additional optical system to allow multiple focusing. Arrangements of this kind require a great deal of space for spectral multiband detection, and their resulting overall size is thus not inconsiderable. In addition, a defocusing effect often occurs therein, so that additional refocusing with the additional optical systemxe2x80x94with reference to the respective spectral regionxe2x80x94is necessary.
It is therefore the object of the invention to configure and develop an apparatus for simultaneous detection of multiple spectral regions of a light beam, in particular for detection of the light beam of a laser scanner in the detection beam path of a confocal microscope, in such a way that a small overall size can be achieved with a simple configuration, the intention being to avoid, to a very large extent, the defocusing effect that occurs in the existing art.
The apparatus of the generic type according to the present invention achieves the aforesaid object by way of an arrangement for spectral spreading of the light beam and an arrangement for splitting the spread beam out of the dispersion plane into spectral regions, and for subsequent detection of the split spectral regions (slit/detector arrangement).
According to the present invention, it has been recognized that simultaneous detection of a plurality of spectral regions of a light beam is readily possible if the light beam is first spectrally spread out and if a splitting of the spread beam out of the dispersion plane is then performed. Splitting of the spread beam out of the dispersion plane is accomplished, according to the present invention, by way of a particular optical arrangement, the partial beams split into spectral regions, or the spectral regions themselves, being detected simultaneously. What is essential here is that the actual splitting into spectral regions is preceded by a spreading of the light beam, so that the splitting out of the dispersion plane can be performed on the spread beam. Multiple focusing with an additional optical system is in any event not necessary here.
As already set forth, according to the present invention two optical arrangements are provided, namely one for spectral spreading of the light beam and another for splitting and subsequent detection. The arrangement for spectral spreading of the light beam can be preceded by a pinhole onto which the incoming light beam is focused; the pinhole can be directly downstream from a laser scanner. What is essential in any case is the focusing of the light beam onto the pinhole arranged in the beam path.
From there, the divergent beam proceeds to the arrangement for spectral spreading of the light beam, this arrangement comprising focusing optical systems and dispersion means. In the interest of particularly simple design, the dispersion means can be embodied as a prism. In further advantageous fashion, a respective focusing optical system, which in turn can comprise a lens arrangement, is arranged before and after the dispersion means or prism.
The divergent beam proceeding from the pinhole to the prism is focused by the focusing optical systems into the slit/detector arrangement (to be explained later), from whence the splitting into spectral regions takes place.
Particularly in the interest of small overall size, reflection means for folding back the spread beam are arranged after the arrangement for spreading the light beam; the reflection means can be a mirror-coated surface or a mirror. In any event, the fact that the spread beam is folded back at least once allows a small overall size for the apparatus as a whole.
As already mentioned earlier, the light beam can be focused into the slit/detector arrangement by way of the focusing optical systems. This slit/detector arrangement is thus arranged in the beam path of the spread beam and comprises reflective surfaces, forming slit diaphragms, which break down the spread beam, on the one hand by slit formation and on the other hand by reflection out of the dispersion plane, into a plurality of partial beams and thus image the individual spectral regions onto the corresponding detectors. In other words, the slit diaphragms provide partial transmission (corresponding to the slit width) of the beam arriving at them, and on the other hand provide reflection at the reflective surfaces provided therein, so that even with one slit diaphragm and two reflective surfaces (one reflective surface on either side to form the slit diaphragm), a breakdown into three partial beams and thus into three spectral regions is possible. This division is performed on the spread beam, out of its dispersion plane. Of course both the partial beam transmitted through the slit diaphragm and the reflected partial beam can once again strike a slit diaphragm and can be broken down there again as explained above. The division into a plurality of partial beams is thus made possible by a multiple arrangement of slit diaphragms having corresponding reflective surfaces.
The split partial beams pass directly to detectors, the number of detectors corresponding to the number of partial beams.
It is furthermore essential for the slit diaphragms provided here that they be placed or arranged approximately at the focus of the spread beam. The reflective surfaces of the slit diaphragms are embodied as mirror-coated surfaces or mirrors; the mirror-coated surfaces can, for example, be vacuum-evaporated in accordance with the support material.
With regard to a concrete embodiment of the slit diaphragms, it is advantageous if the mirror-coated surface is associated with a slit diaphragm jaw forming the slit diaphragm, and if the slit diaphragm jaw is adjustable, or movable or displaceable, in terms of its position which defines the slit diaphragm, the region of the spread beam to be reflected, and optionally the reflection angle. By adjusting the slit diaphragm jaw it is thus possible to define not only the spectral region of the transmitted partial beam and the reflected partial beam, but also the direction in which the reflected partial beams travel. The arrangement of the detectors is thus variable at least within a certain range.
Concretely, the slit diaphragm jaws could be embodied as respective cubic or, for example, also quadrangular bars having an at least partially mirror-coated surface. One of the surfaces then serves, at least partially, as a reflective surface, this being the surface adjacent to the actual slit. A solid glass element, which in accordance with the type of glass used can already offer a total reflection at its surface, is suitable for manufacture of the slit diaphragm jaw. In addition, glass is easy to process and has an extremely low coefficient of thermal expansion, so that temperature-related adjustment of the arrangement is not necessary.
In further advantageous fashion, the slit diaphragm jaws are embodied in the manner of a slider with a rotationally driven spindle and with a corresponding thread. Adjustment of the slit diaphragm jaws can thus be accomplished via actuators that cause an advance and optionally a rotation of the mirror-coated surface of the slit diaphragm jaw. Displacement of the position of the slit diaphragm jaw allows the slit width and the width of the reflected beam, and thus of the respective spectral region, to be adjusted. Adjustment of the angular position of the slit diaphragm jaw and thus the reflection angle makes possible alignment with immovably positioned detectors. The actuators can be any desired manual actuation systems. Electric motors, in particular electric motors with a fine adjustment system, advantageously serve as actuators.
Within the slit/detector arrangement, features can be provided to suppress flare, for example so-called beam traps or stops such as those sufficiently known from the existing art for flare suppression.
Any conventional detectors, preferably photomultipliers, can be used as detectors for the various spectral regions or colors. It is also possible, for example, to use commercially available CCD sensors.
In the interest of a compact design for the apparatus as a whole, it is advantageous if the arrangement for spectral spreading of the light beam and the slit/detector arrangement are carried by a single chassis that is mounted or can be fastened directly to the laser scanner. The slit/detector arrangement with the slit diaphragm jaws provided thereon could be arranged in a housing that can be handled as an insert. The insert could in turn be adjustable in terms of its position, in order to establish the incidence angle and the dispersion plane of the spread beam.
Lastly, it is also conceivable for the housing for the slit/detector arrangement to be largely thermally insulated, specifically in order effectively to eliminate thermal influences on the arrangement therein.